Carbon nanotubes (CNTs) are long, thin cylindrical carbon molecules with novel properties, making them potentially useful in a wide variety of applications (e.g., nano-electronics, optics, materials applications, etc.). CNTs are essentially single sheets of graphite (a hexagonal lattice of carbon) rolled into a cylinder. CNTs range from approximately 0.6 to 5 nanometers (nm) in diameter, and can be as long as a few centimeters. They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat.
CNTs have a very broad range of electronic, thermal, and structural properties that vary based on the different kinds of nanotubes (e.g., defined by its diameter, length, and chirality, or twist). They simultaneously have the highest room-temperature mobility and saturated electron velocity of any known substance.
Conventional field effect transistors (FETs) are non-linear devices. There are two primary sources of non-linearity in conventional FETs. First, conventional FETs have a depletion region in the channel which varies in size with applied gate voltage. As a result, the gate-source capacitance varies with voltage, and charge in the channel is a non-linear function of gate voltage. Second, the carrier velocity is a non-linear function of the electric field. The combination of these two effects results in a drain current that is a non-linear function of the gate voltage.
Linear amplifiers made with conventional FETs burn a lot of power. The standard method of building linear amplifiers from conventional FETs is to use a large source-drain bias. However, the large source-drain bias can result in a large electric field along the length of the channel. As carriers flow down the channel, they gain sufficient energy to stimulate optical phonons. As a result, the carrier velocity saturates and becomes nearly independent of the source-drain and gate biases. However, the total charge in the channel is still a nonlinear function of the gate voltage. The gate bias is then chosen at a point where the second and/or third derivatives of the drain current are minimized. This point varies with device geometry. This approach minimizes the non-linearity of the FET in that it maximizes the second and/or third order intercepts, but a large source-drain voltage is required and a significant amount of power is dissipated generating optical phonons.